The invention relates generally to electrical power switchgear with motor operators and, more particularly, to motor operators for power switches with a drive system that facilitates switch operation by force either from the motor of the operator or such as manually applied force, even for switches at overhead (or pole-top) locations.
Motor operators are widely used in combination with power switches. A variety of operators are in use with various features to permit a switch operation to be performed manually. These have included operators with features for mechanically decoupling the operator's drive system from the motor to allow manual operation. Decoupling has taken a number of different forms. Power switches are applied at a variety of locations including some at surface, or ground level, locations relatively easily accessed for manual decoupling and switch operation and some at overhead (or pole-top) locations less easily accessed.
For example, some overhead switches have a motor operator at or near ground level with a mechanical (reciprocating or torsional) link to a switch drive at the overhead location that may be forty or fifty feet higher. Such an operator is, for example, described in Cleaveland/Price Inc., Bulletin DB-128D09 of 2009. Other motor operators are mounted at pole top locations such as on the switch cross arm. Such an operator is, for example described in Cleaveland/Price Inc., Bulletin DB-38A09 of 2009. The motor operator is housed in an enclosure also containing other power, control and protection elements, including elements for initiating operation from a remote control station. To perform a manual switch operation with that system, a worker removes a hand tool (e.g., a hand crank) from the enclosure whose removal opens a handle interlock switch that in turn opens the motor control circuit so the motor will not operate during manual operation. A decoupler pin, or other mechanical release element, is available for manual removal so a manual switch operation can be performed using the hand tool to apply force to move the mechanical linkage to the overhead switch without requiring manual turning of the motor. When manual operations are completed, replacement of the hand tool and the decoupler pin restores the system for operation by the motor.
Such systems have been quite successful. Recently, however, some interest has developed in equipping overhead switches with motor operators at the pole-top location with only a short mechanical link to the switch. This can, for example, lessen any concerns about dimensional variance of the mechanical linkage over the long life of an installation, minimize ground equipment subject to safety or vandalism concerns, and provide an overall cleaner, uncluttered look to an installation (even though some power supply and control elements can be housed at a surface location, preferably of course well secured in a locked enclosure). While such operators may be similar to the former ground-based units in some respects, e.g., including remotely initiated power operation, if the same features for manual operation are retained there is the problem of accessing the manual elements, such as requiring a worker to climb up to the operator, or use of a lift-truck, which is expensive and troublesome. Among other prior art of switch motor operators with some kind of decoupling for manual operation, whether or not for overhead installations, are those contained in the following U.S. patents (which are merely partially and briefly described).
Evans U.S. Pat. No. 3,980,977, Sep. 14, 1976, illustrates a system in which insertion of a specified hand tool at a particular location of a clutch mechanism in a motor operator disconnects the motor from the mechanism and allows manual rotation of a drive lever that recharges a wound spring operating mechanism.
Ramos et al. U.S. Pat. No. 5,091,616, Feb. 25, 1992, shows a pole-top motor operator and specially designed switch combination with a disconnect linkage manually operable by a hook stick or the like that moves switch-pole housings of the switch.
Sanders U.S. Pat. No. 5,856,642, Jan. 5, 1999, discloses an infinite engagement friction clutch coupled switch operator with selectable engagement and disengagement by a user to allow for manual operation.
Lo et al. U.S. Pat. No. 5,895,987, Apr. 20, 1999, and U.S. Pat. No. 6,025,657, Feb. 15, 2000, presents a switchgear motor operator with a drive including a clutch with a hub and friction discs or an actuator-follower arrangement with opposing actuating and follower surfaces that is subject to an automated control means that responds to a switch operation to reverse the engaging elements to allow manual operation.
Such known art, however useful each may be and with whatever varied tradeoffs each carries with it in terms of high or low cost, convenience, complexity, and susceptibility to inoperability due to a loss of power or functionality, all has a common characteristic in that each necessitates performing an explicit decoupling process, in addition to the merely normal switch opening and closing of a motor operator, either manually or motor driven and either specifically initiated when desired or automatically by a control system.
U.S. Pat. No. 7,026,558 issued Apr. 11, 2006, to Joseph K Andreyo, and assigned to the present assignee, which patent is herein incorporated by reference as though fully set forth, discloses a switchgear motor operator having its motor shaft coupled to the output member of the operator, that connects with the power switch, through a drive assembly with at least one drive element continuously linked to the motor shaft, but not to the output member, and at least another drive element continuously linked to the output member, but not the motor shaft. Temporary engagement of the mentioned drive elements, with motor operation of the power switch, is effected by temporary force transfer parts on the drive elements (e.g., a fixed post on one engaging a spring-loaded cam bar on the other) which inherently disengage following force transfer sufficient to operate the switch. The inherently decoupled state allows immediate straightforward manual operation by an operating member, even when the motor operator is at an overhead switch location, without any turning of the motor or engaging of the temporary force transfer parts during the manual operation. However, it has been found that that the temporary engagement of the aforesaid temporary force transfer parts, i.e., a fixed post on one engaging a spring-loaded cam bar on the other may result in less than the maximum force of the motor being applied to the power switch or less than the force required for ice breaking when ice accumulates on the overhead switch. Reference is made to the aforesaid Cleaveland/Price Inc., Bulletin DB-38A09 of 2009.
Proceeding from this known prior art, it can be regarded as an object of the present invention to provide a motor operator with positive decoupling characteristics for such electrical power switches, but also operates with higher force for ice breaking and operating switches that require such high force.